Electrical wave production



Dec. 18, 1934. w. A. MARRISON ET AL 1,985,046

ELECTRICAL WAVE PRODUCTION Filed March 2, 1934 II H H II II ll MOD.

B.P.F.

MOD.

2a,4a,sa-24a Kc. KC 37 MOD.

2s 46,66-246 wc.

MOD.

24 44,e4-244 K.C.

MOD.

IOO K.

2OK.C.

L.P. FILTE K.C. MOD.

MOD.

MOD.

20,40,617; 12o KL.

|a,as,5a 238 no.

MOD.

|s,se,5s,7e-23s K.C.

MOD.

FILTE FILTER 2.10 Kc. 12 32,52, 72- 2 2 K C- WAMARR/SO/V 4 K.C.GENERATOR INVENTORS- UM Q ATTORN V I4 34 54,74-234 K.C.

MOD.

Patented Dec. 18, 1934 UNITED STATES ELECTRICAL WAVE PaoDUc'rIoN iWarren A Marrison, Maplewood; and Larned A. Meacham Montclair, N. J.,assignors to Bell'- Telephone Laboratories, IncorporatedJ NeW YorkQN.Y., a corporation of New York Application March 2, 1934, Serial No.713,764 I of course, capable of other uses.

An object of the invention is the production of a large number of wavesspaced in frequency with an economy in filtering circuits necessary forseparation of thevarious wave components.

A further object 'is the production of a large number of waves spaced infrequency with a minimum production of spurious or unwantedfrequencies.. a I I A feature of the present invention is a circuitstructure in which the 'wavesiasfinally produced appear in a number'ofseparate circuits'with a frequency spacing sufficiently large .to enablethem to beseparated readily: The final output waves which are closetogether in frequency are produced in difierent'output circuits and donot need to be separated from one another by filtering means. 'j

A more complete understanding of the invention together with its variousobjects and features will be had from thefollowing detailed descriptionwhen read in connection with the ac-' companying drawing in which thesingle figure shows in block diagram the circuit structure of a systemaccording to the invention by which a large number of waves closelyspaced in frequency are produced. l

While the invention is of general application, its mode of applicationwill be readily understood by considering a specific problem as outlined in the accompanying drawing. It isfassumed for illustrativepurposes thattheiproblem is to produce a series of electrical waves witha spacing of 2 kilocycles beginning with-a lower frequency of 12kilocycles and extending-,to-an upper frequency of 250 kilocycles persecond,,as indicated by the final output filters 40, 41,..42, 43, etc.shown at the right-hand side of 1 the figure. It is further assumedthatthese waves are to be produced from a single originating sourceshown at 1 in the lower left corner of the figure, this sourcecomprising a4 kilocycle generator of any suitable type for delivering 'aconstant frequency wave. I

The source of constant 4 kilocycle frequency waves 1 leads to a harmonicgenerator? which may be conveniently of the multi-vibrator type 'ofcircuit well known in the art and which produces in its two outputcircuit branches a 2 kilocycle frequency and multiples thereof. The

5Claims. (01.250-36) Y filter 3 and impressed on the harmonicgenerator 4which is shownafprovided with two -,output branches, one leading toharmonic generaton-E; and'delivering thereto a wave of kilocycles;

the fourth multiple of which is supplied to one input branch ofmodulator7. The otherbranch from, harmonic generator 4 delivers multiples of 20kilocycles up to andincluding kilo cycles throughthe low pass filter 6to the second input branch of the modulator {7 Modulator 7 producesupper and lower sidebands resulting from the modulation of the 400kilocycle-component with the 20, 40-120 kilocycle components from filter6, these sidebands representing com ponents extending; from 280 to 52 0kilocycles with a 20'kilocycle spacing between components.

The output of this modulator -'7 is;supplied; in

multiple to each of the ten modulators 20 to 29 inclusive, 9 v

Another branch from the output o f'modul'ator '7 supplies a 520kilocycle; component to each of two filters- 8 and ;14.- Filter 8 ispreferably a band pass filter of. the crystal type with a highlycomponent iseffectively isolated from all of'the I otherspresent. v ,Thefilters-10tot19 which have to meet ,the mostfrigid requirements,thatg'are placed on any of the filters of the system donot nee'd'tobe ascomplicated as might beexpected. Forexamplejapplicants-have found that afilter comprisingon'ecrystal in series in the circuit with ashunt arm onone or both sides of the crystal, comprising-a condenser, is capable ofdiscriminating between 520 and '522 kilocycle waves with adiscriminationof the order .of 20 or 25 decibels. Each of; the modulators 20 to 29,inclusive, is therefore supplied with a substantially pure'wave ofasingle frequency, namely 512 kilocycles, 514-530 kilocycles,respectively. Consider now the modulator 23,, by way of example. Thismodulator has appliedto it a substantially pure wave component of- 518-kilocycles together-with thirteeri difierentfrequency componentsextending from 280 to 520 kilocycles tenth multiple or 20 kilocycles isselected byinclusive with a spacing of 20 kilocycles, these componentsbeing derived, as previously stated, from modulator 7. Considering onlythe lower sideband components resulting from the action of modulator 23,the highest of these output components is obtained by subtracting 280from 518 kilocycles which gives 238 kilocycles. The lowestof theoutputcomponents (neglecting the 2 kilocycle component which is not used) isfound by subtracting 500 from 518 kilocycles making an 18 kilocyclecomponent. Other components between these extremes are obtained atfrequency intervals of 20 kilocycles. The output leads from modulator 23are shown multipled to two filters 43 and 43, the former of which isselective to the 18 kilocycle component and the latter to the 38kilocycle component. It will be understood that these leads aremultipled to other filters similar to 43 and 43, but not shown in thedrawing, these other filters being selective, respectively, to 58,78-238 kilocycles, respectively. In similar manner modulator 24 hasapplied to it'a' 520 kilocycle component from filter 14 (in this case)and a series of waves from the output of modulator '7 comprisingcomponents 280 to 520 kilocycles with 20 kilocycle spacing. The lowersideband components in the output of modulator 24 comprise, therefore,the components 20, 40, 60-240 kilocycles which appear in the outputleads 34. These leads are shown multipledto a 20- kilocycle'filter 44and a 40 I kilocycle filter 44 and it will be understood that they arealso multipled to other filters not shown in the drawing but selectiveto the other frequencies present in these leads.

In similar manner each of the modulators 20 to 29, inclusive, hasapplied to its input a single high frequency component and a series oflower frequency components whereby there are produ'cedin the output ofeach modulator a series of wave components 20 kilocycles apart. It willbenoted that the filters connected to any one modulator output branchsuch as 33 have a very low requirement placed upon them since they onlyneed to separate between frequencies 20 kilocycles apart, the highest ofwhich is 250 kilocycles. In the most severe case this represents aseparation between components that are spaced apart by about of thefrequencies in question, a requirement easily met by a simple andeconomical type of filter design. Thus, in the example given 120 wavecomponents extending from 12 to 250 kilocycles with a 2 kilocyclespacing are obtained by a circuit arrangement in which the minimumfrequency separation required by thefinal output filters is 20kilocycles.

The ten filters 10' to 19, inclusive, which are required to have highdiscrimination are few in number, representing-in the illustration givenless than 10% of'the number of thefinal output filters. r w By utilizingonly the lower frequency sideband resulting from each of the modulators20 to 29, inclusive, all interference from harmonics of the input wavesis avoided. For example, the lowest input component frequency is 280kilocycles, whereas it will be noted that the highest frequency utilizedis 250 kilocycles so that no interference from the 280 kilocycle wave ora harmonic of it or any other input component is possible.

It will be obvious from the example that has been given that theprinciple of v the invention can be extended to cover widely differentfrequencies and arrangements from those illustrated and described. Themagnitudes given are typical and practicable for supplying carrier wavesto an actual carrier signaling system such as a carrier telephonesystem, but it will be understood that the specific frequenciesmentioned and also the actual number of filters, modulators, etc. to beemployed in any given system can be varied widely to suit requirementsand the values that have been given are to be taken as illustrative andnot as limiting.

What is claimed is:

1. The method of producing a number of waves spaced in frequencycomprising producing a series of waves with a greater frequency intervalthan that of the desired waves, producing a second series of waves ofhigher frequency than the first series and with the desired frequencyspacing, and modulating each of the latter Waves by a plurality of theformer to'produce waves of the desired frequencies.

2. The method of producing a number of waves spaced in frequencycomprising producing a series of waves with a greater spacing than thatof the desired waves; producing a .second series. of waves of higherfrequency than'the first series and with the desired frequency spacing,separating the latter waves :into separate circuits, modulating each ofthe waves so separated by a plurality of waves of the first mentionedseries to produce lower sideband waves of the desired frequencies, andseparating .the resulting waves.

3. In a system forproducing waves of spaced frequencies, means toproduce a first series of waves with a greater frequency spacing thanthat of the desired waves, means to produce a second series of waves ofhigher frequency than the first series and with the desired frequencyspacing, and means to modulate each of the latter waves with a pluralityof the waves of the first series to produce resultant waves of thedesired frequency and frequency spacing.

4. In a wave producing system, a plurality of modulators, circuitsapplying to onemodulato-r a high frequency wave and a series of lowerfrequency waves spaced in frequency to produce resultant lower sidebandWaves of the same frequency spacing but lower than said high frequency,circuits supplying to a second modulator said series of waves and asecond high frequency wave spaced in frequency from said first highfrequency wave by less than the spacing of said series of waves toproduce resultant lower sideband waves overlapping in frequency thefirst mentioned lower sideband waves, and means on the output side ofeach modulator for selecte ing the; different resultant waves.

am a wave producing system, a master source of waves ofv givenfrequency, a first wave translating circuit for producing under controlof'said source a certain series of waves spaced in frequency, a secondwave translating circuit for producing under control of said source asec,- ond series of waves more closely spaced and of higherfrequencythan the first series, and means to modulate each of said latter wavesby a pluralityof said first series of waves to produce waves havingfrequencies lower than either series and with the spacing of said secondseries.

7 WARREN A. {MARRISON LARNED .A. MEACHAM.

